Koontz Lake is an unincorporated community and census-designated place in Starke and Marshall counties in Indiana.

Koontz Lake is located in the northeast corner of Starke County.

[6] The east end of the lake and of the CDP are in western Marshall County.

Indiana State Road 23 passes through the community on the west side of the lake, leading north 4 miles (6 km) to Walkerton, the post office for Koontz Lake addresses, and south the same distance to U.S. Route 30 in Grovertown.

26.5% of all households were made up of individuals, and 13.3% had someone living alone who was 65 years of age or older.